This invention relates to pneumatic tires which will be used primarily in light off-the-road applications. More particularly this invention relates to tires where the environmental impact by the vehicle/tires is to be minimized, while still retaining traction, especially wet traction Examples of such uses are on all terrain vehicles and golf cars and other lawn or garden service vehicles.
In many off-the-road applications, the tires used on a vehicle utilize a wide open tread pattern with axially extending tread lugs which cut into the loose ground surface. Tires which utilize this approach are generally those known in the industry as Agricultural (tractor) tires and Off-the-road (Earthmover, dozers, etc.) tires. These tires are generally used on large vehicles and in applications where the damage or impact to the ground is of a secondary importance to traction.
Some smaller vehicles though, which are used primarily in off-the-road conditions, i.e., not primarily highway use, do not fall into either of the above categories in their use or in their environmental impact. Specifically All Terrain Vehicles (ATV) and golf cars are two such examples. Each uses a light weight vehicle that is primarily driven off the road where not only good traction characteristics are required, but also where the damage to the turf is best kept to a minimum. This is especially true of the golf car tires where much time and money is spent maintaining well conditioned grounds by country clubs and other owners of golf courses.
Damage to such grounds can occur as the tires of the car slip with respect to the turf. The slippage can be increased, and therefore the damage under wet conditions.
It is therefore desirous to produce a tire which will have a minimal impact on the turf of golf courses and other off-the-road applications to thereby reduce the damage thereto and the cost to repair such damage. It is believed that as a goal for such reduction in the damage of the turf that the effect of the tire upon the turf should approximate that of a human foot.
At least one study has indicated that the average human foot exerts 7.5 PSI of pressure while an individual is standing at rest. It is preferable then that in the static footprint, the tire should not exert more than 2.10 times the PSI of that of the average human footprint and preferably less.
The traditional golf car tire is a bias ply tire which is typically a ribbed tire, either with smooth ribs or with blading or sipes. Alternatively, tires have employed repeating block patterns and, in some ATV tires, lugs. The lugs in these tires have traditionally a nonskid which in some cases acts similar to those of the larger Agricultural or Off-the-road tires as they cut or bite into the ground. This can result in damage to turf and other ground conditions which may accelerate erosion.
It therefore would be advantageous to develop a tire which has good traction, especially wet traction, on turf. It is also desirous to provide a tire which has good traction characteristics while having a low environmental impact upon the ground and thereby minimizing the stress on grass blades in order to help assure their survivability.
It is believed that these and other considerations can be accomplished by a low pressure non-belt reinforced pneumatic radial ply tire for light off-the-road use comprising:
a circumferentially extending ground engaging tread portion, said tread portion having a plurality of voids spaced about said tread such that the net-to-gross is in the range of 0.63 to 0.77;
a pair of sidewalls, one said sidewall extending radially inward from each lateral edge of said tread to a bead portion having an inextensible bead therein:
two radial carcass plies, each extending from one said bead to the other said bead portion, said carcass plies comprising a plurality of cords laid at a cord angle from 65.degree. to 85.degree. with respect to the equatorial plane:
wherein the aspect ratio is in the range of 0.40 to 0.75.